Implantable pacemaker/defibrillator devices are well known to the medical profession. One early example of such a device is U.S. Pat. No. 3,857,398 to L. Rubin. The Rubin device utilizes separate circuitries in dealing with the different functions of pacing and defibrillation. There is no provision in the Rubin device for changing the bradycardia standby rate. All of Rubin's bradycardia pacing pulses are apparently delivered at the same rate. Many advances have been made after Rubin in the development of devices and techniques for providing effective medical responses to a variety of heart disorders of arrhythmias.
Recent efforts have resulted in the development of more sophisticated implantable pacing and defibrillating devices. One example of such a device is disclosed in U.S. Pat. No. 4,869,252 to N. L. Gilli, entitled "Apparatus and Method for Controlling Pulse Energy in Antitachyarrhythmia and Bradycardia Pacing Device". This Patent discloses an apparatus which provides bradycardia support pacing at different energy levels, including a higher pulse energy for a period following successful antitachycardia therapy, and a lower level during normal bradycardia support pacing. Capture is more efficient at the higher energy level since the heart has been traumatized by the tachycardia and/or the antitachycardia therapy. In the Gilli patent, again, the bradycardia therapy is delivered at a constant programmed standby rate.
The implantable pacing and defibrillating device disclosed in U.S. Pat. No. 4,940,054 to R. Grevis et al., entitled "Apparatus and Method for Controlling Multiple Sensitivities in Arrhythmia Control System Including Post Therapy Pacing Delay," is another example of a more sophisticated device of this type. Following antitachycardia therapy, which may be antitachycardia pacing or cardioversion/defibrillation, there is a pause or post therapy delay for a period of time substantially greater than a normal standby interval prior to the commencement of bradycardia support pacing. However, when bradycardia support pacing is required after antitachycardia therapy, it is delivered at a constant rate.
A problem that is common to all existing antitachyarrhythmia devices is their failure, after reverting tachycardias, to compensate patients who are dependent on bradycardia support pacing for the hemodynamic compromise resulting from the tachycardia and/or the antitachycardia therapy.
A tachycardia and/or antitachycardia therapy can temporarily reduce the heart's pumping efficiency. If so, the hemodynamic competence of a bradycardia support pacing-dependent patient being paced at a constant standby rate is impaired for as long as the pumping efficiency remains reduced. This can be traumatic to a patient and presents a real problem to some patients that are currently using existing devices.
It is therefore a primary object of the present invention to provide an improved apparatus and a method for treating cardiac arrhythmias which, following reversion from tachycardia, compensate for hemodynamic compromise experienced during tachycardia and/or following antitachycardia therapy.
It is a further object of the invention to provide an improved apparatus and method for treating cardiac arrhythmias which delivers antitachycardia pacing therapy and cardioversion/defibrillation therapy when needed and includes temporarily increasing the bradycardia support pacing rate following the delivery of antitachycardia therapy.
Further objects and advantages of this invention will become apparent as the following description proceeds.